The present invention relates to a solid-state image pickup device, a method of driving the solid-state image pickup device, and an electronic apparatus using such a solid-state image pickup device.
In a solid-state image pickup device, a substantially linear output signal is obtained from a unit pixel with respect to the amount of charge accumulated by photoelectric conversion. A dynamic range of the solid-state image pickup device is uniquely determined by a noise level as well as the quantity of charge which can be accumulated in the unit pixel (saturated charge quantity). That is, the lower limit of the output level of the solid-image pickup device is limited with the noise level and the upper limit thereof is limited with the saturation level. As a result, the dynamic range of the solid-state image pickup device is uniquely determined by the saturated charge quantity and the noise level.
In order to extend the dynamic range, the following technique has been generally employed. That is, a wider dynamic range of the solid-state image pickup device has been attained by combining signals of different sensitivities together, for example combining an image having a comparatively clear low-luminance part taken by a long-time charge accumulation and an image having a comparatively clear high-luminance part taken by a short-time charge accumulation.
As a technology to obtain signals of different sensitivities, two or more unit pixels adjacent to each other are combined into a group so as to correspond to one pixel in an output image while the unit pixels in the group are provided with different sensitivities (see, for example, Japanese Unexamined Patent Application Publication No. 2005-065082).
However, the technology disclosed in Japanese Unexamined Patent Application Publication No. 2005-065082 a plurality of unit pixels in combination is designed to correspond to one pixel to obtain signals with different sensitivities. Thus, a decrease in resolution of an output image may occur in comparison with one in which unit pixels on an imaging surface correspond one-on-one to pixels of the output image.
In addition, there is another technology in which two or more signals with different sensitivities can be obtained from the same pixel (one pixel) while being read from two or more rows at different timing on row-scanning (see, for example, Japanese Unexamined Patent Application Publication No. 2003-198948).
However, in a first example in Japanese Unexamined Patent Application Publication No. 2003-198948, a plurality of signals with different sensitivities is output at different timing points in a row-scanning movement from one pixel. Thus, a frame memory is desired for synchronization of the signals with different sensitivities, while causing increases in size and cost of the device. In addition, in a second example in the above patent document, there is a disadvantage in that a reset noise is placed on a preceding signal because a reset level is output after output of the preceding signal from one pixel.